I've got this bit coming up in my (late renaissance-esque period fantasy) story where the three main characters will be going through this underground labrynth/catacombs/cavern system for a good few days straight. What didn't occur to me until just now is how well campfires would work out underground. What concerns me is the smoke. With nowhere to go, would the smoke become a problem and cause breathing problems, or what? How DO you camp out underground? I know it can get pretty cold, so of course fire would be preferable--especially if they have food rations they have to cook-- but I keep wondering about the fire's smoke and whether it would be a problem. Would they have to only have one in an open chamber rather than an enclosed tunnel (which is what the system mostly consists of)?
Neat as I think it would be to camp out underground to see for myself, unfortunately I don't have that experience.
[[EDIT]]And just as I posted this, the question of what to burn for fire occurred to me. So pretend they have something to burn, as I'll come up with something when the time comes. Then what? [[/EDIT]]